CoGa2O4 Nanoparticles and Films Using a Single Molecular Source
Résumé
Mixed-metal tert-butoxide, [CoGa2(OtBu)8], was employed in the chemical vapor deposition (CVD) and sol-gel processes to obtain thin films and nanoparticles of spinel CoGa2O4 phase, respectively. The appropriate Co:Ga ratio and intact vaporisation (115-120 oC / 10-2 Torr) of the molecular source produced crystalline deposits of CoGa2O4 at relatively low temperatures (~ 500 oC). A clean transformation of the heterometal precursor in spinel oxide of definite composition was supported by TG/DTA analysis that showed no weight loss above 470 oC. The SEM images of CoGa2O4 films showed homogeneous morphology and dense microstructure constituted by nanometric grains (, ~ 35 nm). Hydrolytic decomposition of the precursor produced gels that upon heat-treatment (400 - 1200 oC) formed nanophasic spinel. For comparison, CoGa2O4 was also prepared by complexing Co2+ and Ga3+ ions with glycolate ligands, significant agglomeration effect, broader size dispersion and amorphous domains were observed indicating that low-temperature synthesis of monophasic materials following conventional chemical approaches is hampered by thermodynamic impediments. The UV-Vis spectra of CoGa2O4 particles exhibit characteristic peaks corresponding to 4A2(F) → 4T1(P) transition in the divalent cobalt cation. The magnetization data of the CoGa2O4 nanoparticles showed as expected an antiferromagentic behaviour.
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